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Abstract:

A method of suppressing interference from remote transmitters operating to
a first standard having frequencies overlapping those for a receiver
operating to a second standard is provided. Such interference being
increasingly common as a result of the deployment of multiple wireless
transceivers within electronic devices either supporting multiple
international standards, such as WiFi and WiMAX, or within typical
wireless environments. Advantageously, the invention presents a means of
actively cancelling interference from transmitters operating within the
same frequency range as defined by the standard. The active cancellation
accordingly allows improved performance for systems with very low
received signal powers, such as GPS, in addition to wireless data
communications standards. An exemplary embodiment providing active
cancellation through delaying the portion of the received signal
according to the first standard adjusting both the amplitude and phase by
means of polar modulation prior to summing this signal with the received
signal to provide a receive signal within which the first standard signal
is nulled. Control of the polar modulator being determined in the
exemplary embodiment by minimizing received power after passband limiting
filters.

Claims:

1. A method comprising;providing at least a receiver for receiving a first
signal according to a first wireless standard, the receiver comprising at
least one band-limiting filter of a plurality of band-limiting
filters;receiving at the receiver a second signal according to a second
wireless standard;providing and feeding forward a first cancellation
signal, the first cancellation signal being at least a portion of the
second signal and having at least one of a predetermined time delay,
predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal;combining the first
cancellation signal with the received first signals; andgenerating a
control signal, the control signal for controlling an aspect of the
generation of the first cancellation signal and being generated in
dependence upon a measure of the received signal power after filtering
thereof by the band-limiting filters.

2. A method according to claim 1 wherein,providing the first cancellation
signal comprises generating a down-converted signal generated at least in
dependence upon the portion of the second signal.

3. A method according to claim 2 wherein,providing the down-converted
signal comprises providing the down-converted signal at least one of
prior to and after providing at least one of the predetermined time
delay, predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal.

4. A method according to claim 1 wherein,providing the first cancellation
signal comprises generating at least one of an in-phase baseband signal
and quadrature baseband signal generated at least in dependence upon the
portion of the second signal.

5. A method according to claim 4 wherein,providing the at least one of an
in-phase and quadrature baseband signal comprises providing the at least
one of an in-phase baseband signal and quadrature baseband signal at
least one of prior to and after providing at least one of the
predetermined time delay, predetermined amplitude relationship, and
predetermined phase relationship with respect to the second signal.

6. A method according to claim 1 wherein,generating a control signal
comprises generating the control signal without dependence upon baseband
signals.

7. A method according to claim 1 comprising;determining a state of a
transmitter, the transmitter providing the second signal;generating the
first cancellation signal according to a first state of the transmitter
and generating other than the first cancellation signal in a second state
of the transmitter.

8. A method according to claim 7 wherein,determining a state of the
transmitter comprises receiving a transmitter enable signal.

9. A method according to claim 7 wherein,generating other than the first
cancellation signal comprises turning off the cancellation circuit.

10. A method according to claim 7 wherein,generating other than the first
cancellation signal comprises generating a second cancellation signal.

11. A method according to claim 10 wherein,generating the second
cancellation signal comprises generating the second cancellation signal
according to an aspect of at least one of the first wireless standard and
second wireless standard.

12. A method according to claim 7 wherein,generating other than the first
cancellation signal comprises providing a nulling signal, the nulling
signal having at least one of a predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the transmit signal.

13. A method according to claim 1 wherein,generating a control signal in
dependence upon a measure of the received signal power comprises at least
one of measuring the power of the received signal directly and measuring
the power of a baseband signal generated from a down-conversion of the
received signal.

15. A method according to claim 1 wherein,receiving a second signal
according to a second wireless standard comprises receiving a second
signal having a centre frequency within the frequency range of the first
wireless standard.

16. A method according to claim 1 wherein,providing at least one of a
predetermined amplitude relationship and predetermined phase relationship
is by providing at least one of a Cartesian modulator and a polar
modulator.

17. A method according to claim 1 wherein,combining the cancellation
signal with the received signal comprises providing at least the
cancellation signal and received signal to a low noise amplifier summing
circuit forming a portion of a receiver circuit operating according to
the first wireless standard.

18. A method according to claim 1 wherein,providing the cancellation
signal comprises providing the cancellation signal at least in dependence
upon at least an operating characteristic of at least one of the first
wireless standard, the second wireless standard, the received first
signal and the received second signal.

19. A method according to claim 18 wherein,an operating characteristic is
at least one of a power, a central frequency, a channel number, dynamic
range, sensitivity, and bit error rate.

20. A method according to claim 1 wherein,providing the cancellation
signal comprises providing the calibration signal to at least one of
reduce the total interfering power from the second signal and increasing
at least one of sensitivity and dynamic range of the receiver.

21. A method according to claim 1 wherein,providing a cancellation signal
comprises providing at least one of a passband filter and a tunable
filter, the one of the passband filter and tunable filter for rejecting
the first signal according to the first wireless standard.

22. A method according to claim 1 wherein,providing a receiver according
to the first wireless standard further comprises providing a first band
filter, the first band filter being transmissive to at least signals
according to the first wireless standard.

23. A circuit comprising;at least a receiver for receiving a first signal
according to a first wireless standard and a second signal according to a
second wireless standard; the receiver comprising at least one
band-limiting filter of a plurality of band-limiting filters;a first
cancellation generating circuit for generating and feeding forward a
first cancellation signal in response to a control signal, the first
cancellation signal being at least a portion of the second signal and
having at least one of a predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the second signal;a transmission path for transmitting the first
cancellation signal and combining the first cancellation signal with the
received first and second signals; anda control signal output port for
providing the control signal for controlling an aspect of the generation
of the first cancellation signal and being generated in dependence upon a
measure of the received signal power after filtering thereof by the
band-limiting filters.

24. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit in generating the first cancellation signal provides a
down-converted signal generated at least in dependence upon the portion
of the second signal.

25. A circuit according to claim 24 wherein,the first cancellation signal
generating circuit generates the down-converted signal at least one of
prior to and after providing at least one of the predetermined time
delay, predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal.

26. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit in generating the first cancellation signal provides
at least one of an in-phase baseband signal and quadrature baseband
signal generated at least in dependence upon the portion of the second
signal.

27. A circuit according to claim 26 wherein,the first cancellation signal
generating circuit generates the at least one of an in-phase baseband
signal and quadrature baseband signal at least one of prior to and after
providing at least one of the predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the second signal.

28. A method according to claim 23 wherein,generating a control signal
comprises generating the control signal without dependence upon baseband
signals.

29. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit comprises a transmitter enable port, the transmitter
enable port for receiving a transmitter enable signal generated at least
in dependence upon at least one of the second signal and the transmitter
generating the second signal.

30. A circuit according to claim 29 wherein,the first cancellation signal
generating circuit generates the first cancellation signal according to a
first state of the transmitter and generates other than the first
cancellation signal in a second state of the transmitter.

31. A circuit according to claim 30 wherein,the first cancellation signal
generating circuit in generating the other than the first cancellation
signal is turned off.

32. A circuit according to claim 30 wherein,the first cancellation signal
generating circuit in generating the other than the first cancellation
signal provides a second cancellation signal according to an aspect of at
least one of the first wireless standard and second wireless standard.

33. A method according to claim 30 wherein,the first cancellation signal
generating circuit in generating the other than the first cancellation
signal provides a nulling signal, the nulling signal having at least one
of a predetermined time delay, predetermined amplitude relationship, and
predetermined phase relationship with respect to the transmit signal.

34. A method according to claim 23 comprising,a detector circuit, the
detector circuit connected to the control signal output port and
generating a control signal in dependence upon at least one of measuring
the power of the received signal directly and measuring the power of a
baseband signal generated from a down-conversion of the received signal.

36. A circuit according to claim 23 wherein,the second signal according to
the second wireless standard comprises a wireless signal having a centre
frequency within the frequency range of the first wireless standard.

37. A circuit according to claim 23 comprising;the first cancellation
signal generating circuit comprises providing at least one of a coupler,
a bandpass filter, a tunable filter and a cancellation circuit integrated
with at least one of a circuit and a receiver circuit.

38. A circuit according to claim 37 wherein,at least one of the circuit
and the receiver circuit comprises providing an integrated circuit being
manufactured using a semiconductor technology based upon at least one of
silicon, silicon-germanium, gallium arsenide, indium phosphide, gallium
nitride and polymers.

39. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit comprises providing at least an integrated circuit,
the integrated circuit being manufactured using a semiconductor
technology based upon at least one of silicon, silicon-germanium, gallium
arsenide, indium phosphide, gallium nitride and polymers.

40. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit comprises providing at least one of a Cartesian
modulator and a polar modulator.

41. A circuit according to claim 23 comprising,a low noise amplifier
summing circuit, the low noise amplifier summing circuit having a first
input port for receiving the first cancellation signal, a second input
port for receiving the received signal, and a sum output port for
providing a summed output signal in dependence upon at least the first
cancellation signal and received signal.

42. A circuit according to claim 31 wherein,the low noise amplifier
summing circuit forms a portion of the receiver circuit operating
according to the first wireless standard.

43. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit provides the first cancellation signal in dependence
upon at least an operating characteristic of at least one of the first
wireless standard, the second wireless standard, the received first
signal and the received second signal.

44. A circuit according to claim 43 wherein,an operating characteristic is
at least one of a power, a central frequency, a channel number, dynamic
range, sensitivity, and bit error rate.

45. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit provides at least one of a reduction in the total
interfering power from the transmitter within a frequency band according
to the first wireless standard and an increase of at least one of
sensitivity and dynamic range of the receiver.

46. A circuit according to claim 23 wherein,the first cancellation signal
generating circuit comprises at least one of a passband filter and a
tunable filter, the one of the passband filter and tunable filter for
rejecting the first signal according to the first wireless standard.

47. A circuit according to claim 23 wherein,the receiver according to the
first wireless standard further comprises a first band filter, the first
band filter being transmissive to at least signals according to the first
wireless standard.

48. A computer readable medium having stored therein data according to a
predetermined computing device format, and upon execution of the data by
a suitable computing device a method of improving a receiver is provided,
comprising:providing at least a receiver for receiving a first signal
according to a first wireless standard, the receiver comprising at least
one band-limiting filter of a plurality of band-limiting
filters;receiving at the receiver a second signal according to a second
wireless standard;providing and feeding forward a first cancellation
signal, the first cancellation signal being at least a portion of the
second signal and having at least one of a predetermined time delay,
predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal;combining the first
cancellation signal with the received first signals; andgenerating a
control signal, the control signal for controlling an aspect of the
generation of the first cancellation signal and being generated in
dependence upon a measure of the received signal power after filtering
thereof by the band-limiting filters.

49. A computer readable medium according to claim 48 having stored therein
data according to a predetermined computing device format, and upon
execution of the data by a suitable computing device a method of
improving a receiver is provided, comprising:determining a state of a
transmitter, the transmitter providing the second signal;generating the
first cancellation signal according to a first state of the transmitter
and generating other than the first cancellation signal in a second state
of the transmitter.

50. A computer readable medium according to claim 48 having stored therein
data according to a predetermined computing device format, and upon
execution of the data by a suitable computing device a method of
improving a receiver is provided, comprising:providing the first
cancellation signal comprises generating a down-converted signal
generated at least in dependence upon the portion of the second signal.

51. A computer readable medium having stored therein data according to a
predetermined computing device format, and upon execution of the data by
a suitable computing device a circuit is provided, comprising:at least a
receiver for receiving a first signal according to a first wireless
standard and a second signal according to a second wireless standard; the
receiver comprising at least one band-limiting filter of a plurality of
band-limiting filters;a first cancellation generating circuit for
generating and feeding forward a first cancellation signal in response to
a control signal, the first cancellation signal being at least a portion
of the second signal and having at least one of a predetermined time
delay, predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal;a transmission path for
transmitting the first cancellation signal and combining the first
cancellation signal with the received first and second signals; anda
control signal output port for providing the control signal for
controlling an aspect of the generation of the first cancellation signal
and being generated in dependence upon a measure of the received signal
power after filtering thereof by the band-limiting filters.

52. A computer readable medium according to claim 51 having stored therein
data according to a predetermined computing device format, and upon
execution of the data by a suitable computing device a circuit is
provided, comprising:the first cancellation signal generating circuit
comprises a transmitter enable port, the transmitter enable port for
receiving a transmitter enable signal generated at least in dependence
upon at least one of the second signal and the transmitter generating the
second signal.

53. A computer readable medium according to claim 51 having stored therein
data according to a predetermined computing device format, and upon
execution of the data by a suitable computing device a circuit is
provided, comprising:the first cancellation signal generating circuit in
generating the first cancellation signal provides a down-converted signal
generated at least in dependence upon the portion of the second signal.

Description:

FIELD OF THE INVENTION

[0001]The invention relates to cancelling interference within wireless
receivers from wireless transmitters operating on overlapping standards,
and more particularly to integrated circuit implementations.

BACKGROUND OF THE INVENTION

[0002]In recent years, the use of wireless and RF technology has increased
dramatically in portable and hand-held units, where such units are
deployed by a variety of individuals from soldiers on the battlefield to
a mother searching for her daughter's friend's house. The uses of
wireless technology are widespread, increasing, and include but are not
limited to telephony, Internet e-mail, Internet web browsers, global
positioning, photography, and in-store navigation. Additionally, devices
incorporating wireless technology have expanded to include not only
cellular telephones, but Personal Data Analyzers (PDAs), laptop
computers, palmtop computers, gaming consoles, printers, telephone
headsets, portable music players, point of sale terminals, global
positioning systems, inventory control systems, and even vending
machines.

[0008]WiFi (WLAN) communication has enjoyed overwhelming consumer
acceptance worldwide, generally as specified in IEEE 802.11a (operating
in the frequency range of 4900-5825 MHz) or IEEE 802.11b and IEEE 802.11g
specifications (operating in the range 2400-2485 MHz). These standards
seem destined to survive and thrive in the future, for example with the
IEEE 802.11n MIMO physical layer. The 802.11 value proposition is the
provision of low cost, moderate data communication/transport rates and
simple network function.

[0009]WiMAX (WMAN) communication is also preparing to deploy massively
worldwide, especially as IEEE 802.16e (operating at two frequency ranges,
the first being 2300-2690 MHz, and the second of 3300-3800 MHz). The IEEE
802.16e value proposition is the provision of moderate cost and high data
communication/transport rates at high quality of service, which requires
higher system performance and complexity.

[0010]As a result, it is highly likely that many applications and devices
will occur where there is need to either support both WiMAX and WiFi
services, such as two transceivers within a single device typically being
co-located a few centimeters apart, or provide sustained operation within
a multi-transmitter environment. As such a potential difficulty arises if
the IEEE 802.16e WiMAX transceiver tries to operate in the first, lower
frequency band of 2300-2690 MHz, and is co-located or close to an IEEE
802.11b/g WiFi transceiver. Although the IEEE 802.16e spectrum is
segmented, into two bands, the lower 2300-2397.5 MHz and upper 2496-2690
MHz, these straddle the IEEE 802.11b/g band of 2400-2485 MHz closely,
giving negligible guard bands of unused spectrum between the two services
to prevent mutual interference.

[0011]Furthermore, although IEEE 802.16e transceivers employ
transmit/receive duplexing this is synchronized "globally" throughout the
area served by each base station, the transmit/receive duplexing of IEEE
802.11b/g transceivers is negotiated locally with each independent
network access point. As there may be many IEEE 802.11b/g network access
points within the transmission zone of one IEEE 802.16e base station, and
the two systems operate completely independently. The co-located units
will therefore see a varying combination of IEEE 802.11b/g or IEEE
802.16e transmitters/receivers at any given time.

[0012]At present, there are no aspects of these IEEE 802.11b/g and IEEE
802.16e standards that address the collocation and
interaction/interference of such collocated systems. Considering prior
art approaches to removing interference of multiple transceivers, then
solutions would appear to be time separation, frequency separation,
filtering, passive interference, and localized device control.
Considering these in order:

[0013]Time Separation: An exemplary embodiment of time separation would be
to force IEEE 802.11 devices not to transmit whilst an IEEE 802.16 device
receiving, or vice-versa. However, this requires the Media Access Control
(MAC) and higher layers of the WiFi and WiMAX systems to interact, which
is not facilitated within existing systems, and would fundamentally
reduce aggregate throughput in both systems;

[0014]Frequency Separation: An exemplary embodiment of frequency
separation would be to provide "bar" operation, and thereby clear,
frequency bands within both IEEE 802.11 and IEEE 802.16 systems near the
band boundaries. However, frequency separation wastes spectrum in one or
both systems and reduces aggregate throughput;

[0015]Filtering: Filtering and/or duplexing the IEEE 802.11 and IEEE
802.16 systems away from each other, without impacting aggregate
throughput, requiring MAC or higher interactions etc. The limited
clearance between the frequency bands of the two systems requires
impractically high-order filters. For example, near 2400 MHz the last
WiMAX channel is 2397.5 MHZ and the first WiFi channel is 2412 MHz. For
an attenuation of ΛdB in the stop band of the filter, with a stop
band frequency of I(s), and a passband frequency of I(p) then the order,
η, of the required filter is given by:

=Λ/{20*log[I(s)/I(p)]} (1)

[0016]For Λ=30, I(s)=2412 MHz, and I(p)=2397.5 MHz, the required
filter order η is 573! Such filters, even if feasible could not be
integrated into the low cost semiconductor circuits being provided for
the WiFi and WiMAX transceivers, increasing costs, degrading performance,
increasing footprint and packaging complexity etc. Further, such
filtering cannot filter out IEEE 802.11 (WiFi) leakage because it is
in-band for the IEEE 802.16 (WiMAX) receiver;

[0017]Passive Interference: Originating from radar infrastructure, the
approach introduces a predetermined portion of the transmitted signal
from an antenna into the receive path of a collocated second antenna.
Whilst, such an approach does not waste spectrum in one or both systems,
nor does it reduce aggregate throughput, such approaches within the prior
art do not support either a remote transmitter, such as another user
within the same coffee shop, nor multiple transmitters, such as several
other customers within a coffee shop, such scenarios being typical for
today's mobile devices with multiple local transmitters interacting with
a receiver. Further the proliferation of multi-standard devices will also
increased occurrences where two transceivers are collocated or
monolithically integrated.

[0018]Localized Device Control. As noted supra the MAC and higher layers
of the WiFi and WiMAX systems do not interact at the overall network
level. However, it is reasonable to assume that when these two
transceivers are within a single device, such as a laptop computer, that
the IEEE 801.11b/g and IEEE 801.16e modems are mutually aware as they are
probably controlled from the same PCI bus. Hence, a "trick" could be to
have either the IEEE 801.11b/g or IEEE 801.16e modems take priority and
force the other "off the air" temporarily; essentially an extreme variant
of time separation. For example, the IEEE 801.16e modem could "pose" as
the closest network access point, force the IEEE 801.11 b/g modem to
associate with it on channel 6 (or channel 7 in European installations)
and then unassociated after IEEE 801.16e reception is complete. Such
association being a logical connection between the mobile station (MS)
and access point (AP) which is formally defined within the IEEE 802.11
standard, such associations normally occurring at power on of the MS or
when it re-discovers an AP after temporarily losing touch.

[0019]The difficulty with this is that it wastes most, or all, of the IEEE
802.11b/g band during the IEEE 802.16e operation. If the WiFi service is
forced off the air simply because WiMAX is being used nearby, the
bandwidth is available from the point of view of the WiFi AP, but cannot
be used by the WiFi MS because of local conditions. Further it imposes
additional transmit/receive protocol overhead and complexities into the
communications. IEEE 802.11 is designed with a fairly simple arrangement
whereby the MS and AP can agree on who will talk or listen at what times,
and what information is transmitted in what order. It is not designed to
synchronize with any other system and these complexities will result in
association and throughput rates being significantly worse than normal
design values.

[0020]As such none of the prior art approaches provide a solution that
does not waste spectrum in one or both systems, nor reduces aggregate
throughput. Further, such prior art approaches are particularly adapted
to network environments wherein IEEE 802.11b/g and IEEE 802.16e modems
are relatively stationary allowing protocols to be established and
utilized. However, today's wireless environments are not stationary for
significant periods of time, and such networks are projected to become
even less so as ad-hoc networking architectures become more common due to
the elimination of significant network planning requirements and
eliminating significant infrastructure costs. As such portable devices
with multi-standard modems (such as IEEE 802.11b/g and IEEE 802.16e) will
continually adjust to achieve network access and provide active leakage
from one modem to another as the local environment changes.

[0021]Furthermore the prior art approaches do not support the emergence of
many consumer orientated electronic devices that operate with collocated
or spatially close transmitters on multiple standards. Additionally,
requirements for an active interference cancellation scheme within such
high volume, low cost electronic devices include adapting to changes in
the wireless environment, such as the rapid addition of a new transceiver
or fast changes in the local environment of the electronic devices and
their locations, and compatibility with the integrated circuit chip set
providing the transceiver functionality.

[0022]It would be further advantageous if the active interference
cancellation approach utilized low power control and adaptation
techniques to enhance battery lifetime for mobile devices supporting the
collocated systems.

SUMMARY OF THE INVENTION

[0023]In accordance with the invention there is provided a method of
reducing interference in a receiver, comprising: [0024]providing at
least a receiver for receiving a first signal according to a first
wireless standard, the receiver comprising at least one band-limiting
filter of a plurality of band-limiting filters; [0025]receiving at the
receiver a second signal according to a second wireless standard;
providing and feeding forward a first cancellation signal, the first
cancellation signal being at least a portion of the second signal and
having at least one of a predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the second signal; [0026]combining the first cancellation signal with
the received first signals; and [0027]generating a control signal, the
control signal for controlling an aspect of the generation of the first
cancellation signal and being generated in dependence upon a measure of
the received signal power after filtering thereof by the band-limiting
filters.

[0028]In accordance with another embodiment of the invention there is
provided a circuit for reducing interference in a receiver, comprising:
[0029]at least a receiver for receiving a first signal according to a
first wireless standard and a second signal according to a second
wireless standard; the receiver comprising at least one band-limiting
filter of a plurality of band-limiting filters; [0030]a first
cancellation generating circuit for generating and feeding forward a
first cancellation signal in response to a control signal, the first
cancellation signal being at least a portion of the second signal and
having at least one of a predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the second signal; [0031]a transmission path for transmitting the
first cancellation signal and combining the first cancellation signal
with the received first and second signals; and [0032]a control signal
output port for providing the control signal for controlling an aspect of
the generation of the first cancellation signal and being generated in
dependence upon a measure of the received signal power after filtering
thereof by the band-limiting filters.

[0033]In accordance with another embodiment of the invention there is
provided a computer readable medium having stored therein data according
to a predetermined computing device format, and upon execution of the
data by a suitable computing device a method of improving a receiver is
provided, the method comprising: [0034]providing at least a receiver
for receiving a first signal according to a first wireless standard, the
receiver comprising at least one band-limiting filter of a plurality of
band-limiting filters; [0035]receiving at the receiver a second signal
according to a second wireless standard; providing and feeding forward a
first cancellation signal, the first cancellation signal being at least a
portion of the second signal and having at least one of a predetermined
time delay, predetermined amplitude relationship, and predetermined phase
relationship with respect to the second signal; [0036]combining the first
cancellation signal with the received first signals; and [0037]generating
a control signal, the control signal for controlling an aspect of the
generation of the first cancellation signal and being generated in
dependence upon a measure of the received signal power after filtering
thereof by the band-limiting filters.

[0038]In accordance with another embodiment of the invention there is
provided a computer readable medium having stored therein data according
to a predetermined computing device format, and upon execution of the
data by a suitable computing device a circuit is provided, comprising:
[0039]at least a receiver for receiving a first signal according to a
first wireless standard and a second signal according to a second
wireless standard; the receiver comprising at least one band-limiting
filter of a plurality of band-limiting filters; [0040]a first
cancellation generating circuit for generating and feeding forward a
first cancellation signal in response to a control signal, the first
cancellation signal being at least a portion of the second signal and
having at least one of a predetermined time delay, predetermined
amplitude relationship, and predetermined phase relationship with respect
to the second signal; [0041]a transmission path for transmitting the
first cancellation signal and combining the first cancellation signal
with the received first and second signals; and [0042]a control signal
output port for providing the control signal for controlling an aspect of
the generation of the first cancellation signal and being generated in
dependence upon a measure of the received signal power after filtering
thereof by the band-limiting filters.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]Exemplary embodiments of the invention will now be described in
conjunction with the following drawings, in which:

[0044]FIG. 1 illustrates an exemplary scenario for collocated mobile
communications systems within a device operating according to two
different standards.

[0045]FIG. 2 illustrates a prior art interference cancellation scheme for
wherein the transmitter signal can be provided to the receiver.

[0046]FIG. 3 illustrates an exemplary first embodiment of the invention
for active cancellation of a WiFi transmitter within a WiMAX receiver.

[0047]FIG. 4A illustrates an exemplary spectrum of a WiFi transmission
signal from a first system operating simultaneously with a WiMAX
transmission signal.

[0048]FIG. 4B illustrates an exemplary spectrum of a cancellation null
according to an exemplary embodiment of the invention positioned to align
with the WiFi transmission signal from a first system operating
simultaneously with a WiMAX transmission signal.

[0049]FIG. 5 illustrates an exemplary spectrum of a WiFi transmission
signal from a first system operating simultaneously with a WiMAX
transmission signal wherein a cancellation null according to an
embodiment of the invention is aligned with the second signal.

[0050]FIG. 6 illustrates an exemplary two-dimensional binary search for
the optimum coefficients of the coefficient engine driving a Cartesian
modulator providing the amplitude and phase adjustment of the transmitter
signal applied to cancel the transmitter leakage.

[0051]FIG. 7 illustrates an exemplary flow diagram for calibrating an
active cancellation circuit according to an embodiment of the invention
for transmission frequencies of the WiFi standard.

[0053]FIG. 9A illustrates an exemplary embodiment for actively cancelling
the leakage between a WiMAX transmitter and a GPS receiver.

[0054]FIG. 9B illustrates the power spectral density spectrum for a system
operating according to the embodiment presented in respect of FIG. 9A.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0055]FIG. 1 illustrates an exemplary scenario for transmitter
interference from a WiFi transceiver 130 to a WiMAX transceiver 150, both
transceivers being located within a single device 100.

[0056]As shown the WiFi transceiver 130 comprises a WiFi antenna 140, for
receiving and transmitting data over the WiFi carrier 145 according to an
IEEE 802.11b or an IEEE 802.11g standard operating in the range 2400-2485
MHz. Shown for the WiFi transceiver 130 are transmit signal input port
130B, which receives the data for transmission encoded onto the
appropriate channel within the WiFi frequency range, and is coupled to
the WiFi power amplifier 120 for boosting and feeding forward to the WiFi
antenna 140. The WiFi antenna 140 is also coupled to a WiFi receiver
amplifier 110, which receives WiFi signals from the WiFi antenna 140,
boosts them with low noise and high gain due to the low received power
and couples this signal to the WiFi receiver port 130A.

[0057]Also the WiMAX transceiver 150 is electrically coupled to a WiMAX
antenna 180, for receiving and transmitting data over the WiMAX carrier
185, according to the IEEE 802.16e standard, operating at the lower of
the two frequency ranges, 2300-2690 MHz. Shown for the WiMAX transceiver
150 are transmit signal input port 150B, which receives the data for
transmission encoded onto the appropriate channel within the WiMAX
frequency range, and is coupled to the WiMAX power amplifier 170 for
boosting and feeding forward to the WiFi antenna 180. The WiFi antenna
180 is also coupled to a WiMAX receiver amplifier 160, which receives
WiMAX signals from the WiMAX antenna 180, boosts them with low noise and
high gain due to the low received power and couples this signal to the
WiMAX receiver port 150A.

[0058]Within the representative embodiment when the WiFi transceiver 130
and WiMAX transceiver 150 are within a single device 100, the spacing
between antennae is often small, on the order of a few centimeters.
Therefore leakage from the WiFi antenna 140 into the WiMAX antenna 180
can occur, giving rise to issues for the receiver as WiMAX receive
signals are now interfered with high power interference from the WiFi
signal within the same frequency range. Further, placement of the
multi-standard single device 100 increases this leakage, for example
placement of the single device 100 on a table surface, close to a users
head, and next to a window. Each of these and other common placements
results in dynamic adjustment in the leakage from one antenna to another.
Further, it would be apparent that within other embodiments where a
device only houses the WiMAX transceiver 150, interference from local
WiFi transceivers within other devices, and even the local base station,
could arise.

[0059]A typical implementation of WiFi transceiver 130 and WiMAX
transceiver 150 within a multi-standard single device 100 is such that
the WiFi transceiver 130 operates at +18 dBm according to the IEEE
801.11b/g standard, and that the WiFi antenna 140 and WiMAX antenna 180
are designed as small, cheap, omni-directional antennas that have very
little directional or frequency isolation between them, and hence a
typical leakage of about 20-25 dB is expected at 2500 MHz. Since both
antennas are often fixed with respect to each other and with respect to
electrically significant metal and dielectric masses nearby, the WiFi
transceiver 130 presents a signal of approximately -2 dBm to the WiMAX
transceiver 150, whereas the WiMAX receiver 150 operates with a signal as
low as -70 dBm according to the IEEE 802.16e specification. Even other
transceivers within the local environment are likely to present sources
of interference which even if at -30 dBm is significant with respect to
the WiMAX signal levels.

[0060]Not only might the WiFi (IEEE 802.11b/g) signal saturate or even
potentially overload the WiMAX receiver amplifier 160 but other channel
leakages, that are potentially at -30 dBc and -50 dBc, respectively
according to IEEE 802.11b, could appear directly in-band for the WiMAX
(IEEE 802.16e) signals in some scenarios. As such, these other channel
leakages, at -32 dBm and -52 dBm respectively would present an
intractable instantaneous dynamic range problem. Such a dynamic range
problem is a situation where a wanted signal at very low level is
received simultaneously with an interfering signal at much higher level,
the dynamic range being the difference between the very low receiver
noise floor required to receive the wanted signal and simultaneously the
very high receiver distortion threshold required to prevent the
interfering signal from clipping the receiver. An intractable dynamic
range problem is one in which the interferer is at or near a same
frequency as the wanted signal, and therefore cannot be filtered out.

[0061]FIG. 2 illustrates a prior art interference cancellation scheme for
a duplex transceiver 200 employing a single antenna. 270. The duplex
transceiver 200 is implemented for the UMTS standard supporting a full
duplex mode unlike the GSM standard. In the UMTS full duplex mode, a
chronological overlap between the transmission and reception modes of
operation is permitted during operation. A signal for transmission is
applied to transmitter port 201 from which it is electrically coupled to
the transmitter output power amplifier stage 210. The output signal from
the transmitter output power amplifier stage 210 is coupled via a
transmission band-transmitting filter 222 and duplexer 275 to the antenna
270 for transmission. A pre-determined portion of the output power of the
transmitter output power amplifier stage 210 is coupled to compensation
element 280.

[0062]A receive signal coupled from the antenna 270 is then coupled via
the duplexer 275 to the reception band transmission filter 224. At this
point the predetermined portion of the output power of the transmitter
output power amplifier stage 210 is applied along with the receive signal
from the reception band transmission filter 224 to the reception
pre-amplifier 230. The output signal of the reception pre-amplifier 230
is then applied to summation node 260. The reference mixing signal
applied to the summation node 260 is coupled from the summation node
input port 202. A first output signal of the summation node 260, which is
part of a second receiver 265, is then electrically coupled to a simple
bandpass filter 226 for subsequent processing and recovery of the encoded
data. If we consider the mixing reference signal applied to the summation
node port 202 to be I(vco) and the received signal from the reception
pre-amplifier 230 to be I(dup) then the signal provided from the simple
bandpass filter 226 is given by:

(itrx)=±I(rx)±I(vco). (1)

[0063]A second output signal of the summation node 260 is then coupled to
the bandpass filter 228 of the second receiver 265 which provides a
signal given by:

(iftx)=±I(dup)±I(vco). (2)

[0064]This signal is then coupled to the second receiver amplifier 240 and
a detector 250. The output signal of the detector 250 is an amplitude of
the receive signal as measured by the narrowband detection circuit
implemented within the second receiver 265. This amplitude of the receive
signal is applied to a controller unit 290 which provides control
signaling to compensation element 280. Additional control settings are
provided to control unit 290 from a control bus port 295.

[0065]In operation, the prior art circuit provides an adaptive control
based on a voltage measurement at the receiver antenna 270, the
compensation element 280 adjusting the phase and amplitude of the
transmitted signal in such a way that this measured voltage is minimized.
As such the prior art relies upon a predetermined temporal relationship
between the "leakage" as a result of contact or close proximity of the
antenna to conductive objects or the human body. As such the prior art
does not consider any variations within the temporal aspects of the
leakage or that leakage causing degradation of reception is other than
from the duplex transceiver 270 itself.

[0066]It would also be apparent to one skilled in the art that whilst the
interference cancellation approach presented in FIG. 2 can be employed to
address interference from a co-located transceiver, such as presented in
FIG. 1 with the single device 100 housing both WiFi transceiver 130 and
WiMAX transceiver 150 this solution cannot handle remote transmitters.
Further, the WiFi transceiver 130 and WiMAX transceiver 150 in order to
support the additional circuitry and interconnections cannot be existing
supplied discrete modules. As such the prior art approach works only with
new designs of WiFi transceiver 130 and WiMAX transceiver 150.

[0067]FIG. 3 illustrates a first representative embodiment of the
invention for active cancellation of a WiFi transmitter within a WiMAX
transceiver 300. As shown the WiMAX transceiver 300 is connected to an
antenna 340, which receives wireless signals 350 from the local
environment. According to this first representative embodiment the
wireless signals 350 comprises WiMAX signals including a desired channel
for data in addition to interference from WiFi signals. The WiMAX
transceiver 300 receives data for transmission at input port 300E and
boosts this with the transmit amplifier 360, which is electrically
coupled to the antenna 340.

[0068]Signals received from antenna 340 are initially electrically coupled
to a splitter 330. A first portion of the received signal is coupled from
the splitter 330 to a first filter 370 which has been implemented to
provide filtering of the wireless spectrum according to the IEEE 802.16e
standard and is operating at the lower of the two frequency ranges,
namely 2300-2690 MHz. Such a filter optionally being part of a
conventional prior art WiMAX receiver circuit.

[0069]From the first filter 370 the filtered wireless signals are fed to
the receiver amplifier 390 via a summation node 380 {SJK--perhaps
summation node is a better descriptor than mixer throughout}. As such
apart from the summation node 380 this signal path representing a typical
receiver path of a prior art WiMAX receiver circuit. From the receiver
amplifier 390 the amplified received and filter wireless signals are
coupled to a second passband limiting filter 315, then to a coupler 325
wherein a portion is directed to a power detector 335, the other port of
the coupler 325 being electrically coupled to the output port 300D. The
output of the power detector 335 is coupled to a coordinate generator 345
at its input port 345D.

[0070]A second portion of the received signal is coupled from the splitter
330 to a second filter 320, which is intended to filter according to the
IEEE 802.11b/g standards, and as such is bandpass filter for 2400-2485
MHz. It would be apparent to one skilled in the art that the second
filter 320 can be implemented with sharp transition bands due to the
relatively small fractional bandwidth of 3.5% (being a bandwidth of 485
MHz at centre frequency of 2442.5 MHz). As such the filter 320 can
provide high isolation to WiMAX signals according to the IEEE 802.16e
specification within the bands adjacent to the 2400 MHz-2485 MHz region.
The WiFi signals passed by the second filter 320 are then electrically
coupled to a delay circuit 355, the delay circuit 355 applying an
appropriate delay to the second portion of the received signal. The
output of the delay circuit 355 is then electrically coupled to a polar
modulator 310 that provides adjustment of both the magnitude and phase of
signals provided to it, and provides the adjusted output from the polar
modulator 310 to the summation node 380. As such the summation node
combines the output of the first filter 370, which is a combination of
the WiMAX and WiFi signals present within the frequency range 2300-2690
MHz, with the attenuated and phase shifted output of the second filter
320, being the WiFi signals present within the 2400-2485 MHz range.
Accordingly it would be apparent that with appropriate adjustment of
phase and magnitude by the polar modulator 310 that this mixing results
in a cancellation of the signals present within the 2400-2485 MHz region,
reducing significantly the interference from these WiFi signals with the
desired WiMAX signals.

[0071]As shown within FIG. 3 the polar modulator 310 is provided with
first and second control inputs at ports 310A and 310B, and the delay
circuit 355 is provided with a control input at port 355A. The first
control signal port 310A is electrically connected to a first output port
of the coordinate generator 345, which is port 345A. The second control
signal port 310B is electrically connected to a second output port of the
coordinate generator 345, which is port 345B. The control port 355A of
the delay circuit 355 is electrically connected to the third output port
of the coordinate generator 345, which is port 345A. In this exemplary
embodiment therefore the coordinate generator 345 controls the polar
modulator 310 such that the measured power at the power detector 335 is
reduced, thereby minimizing the interfering signal within the WiMAX
receiver. {As with the feed-forward there is in principle no collocated
transmitter then I would assume no TXEN signal available. The nearest
equivalent would be setting a threshold for the power within the
feed-forward portion which is being adjusted by the polar modulator . . .
but have added an element in text to cover either scenario)

[0072]It would be apparent to one skilled in the art that the invention
provides for the cancellation of the interfering WiFi signal presented
within the wireless signals 350 received by the antenna 340. The
feed-forward cancellation approach outlined within this first embodiment
advantageously requiring no communication with interfering transmitters,
may be implemented with standard circuit elements such as a WiFi bandpass
filter for the second filter 320 and a polar modulator 310. The polar
modulator 310 further advantageously presenting a means of providing the
required amplitude and phase adjustment with low power consumption, a
requirement of mobile device applications.

[0073]The polar modulator 310 provides modulation of a signal in a manner
analogous to quadrature modulation but relying on polar co-ordinates, r
(amplitude) and θ (phase). Whereas quadrature modulators require a
linear RF power amplifier, creating a design conflict between improving
power efficiency or maintaining amplifier linearity, this is not a
limitation within polar modulation, which allows highly non-linear
amplifier architectures to be employed with high power efficiency. Such
amplifiers are useful as polar modulation operates with an input signal
of the amplifier of "constant envelope", i.e. containing no amplitude
variations. Hence, amplitude control is achieved by directly controlling
the gain of the power amplifier, which is not undertaken in amplitude
modulation wherein the amplifier is operated at fixed gain.

[0074]In a polar modulation system, the power amplifier input signal
varies only in phase. Amplitude modulation is then accomplished by
directly controlling the gain of the power amplifier. Thus a polar
modulator allows the use of highly non-linear power amplifier
architectures such as Class E and Class F, these being highly efficient
switching power amplifiers.

[0075]A first benefit of this active cancellation arrangement is that the
WiFi interference is removed at the input block to the WiMAX receiver,
reducing its required instantaneous dynamic range, and sensitivity to the
WiMAX signals is not impaired beyond a small thermal penalty imposed by
the summation node 380. Beneficially this active cancellation not only
addresses leakage from the main lobe of the interferer solving the WiMAX
receiver clipping problem, but also spurs and transmitted noise, are at
least partially cancelled.

[0076]It would be beneficial at this point to address performance limits,
as with any physical implementation active cancellation has some
performance limits. Thermal noise floor has been mentioned above. The
other limits can be understood by realizing that cancellation is
essentially a subtraction of two signals to produce an error signal
ξ(t) at the input port of the WiMAX receiver amplifier 390, typically
a low-noise amplifier (LNA). Considering simplistically that the
reference signal is cos (ωt) then ξ(t) can be expressed as:

(t)=cos (ωt)-[α*cos (ω(t-δ))+β)] (3)

[0077]Where [α*cos (ω(t-δ))+β] is the cancellation
signal provided through the coupler 330, second filter 320 and polar
modulator 310 combination. Here ω=2πf, the angular frequency,
α is the amplitude scaling of the polar modulator 310, β is
the phase shift of the polar modulator, and δ is the delay
difference introduced as a result of the WiFi filtered path, comprising
second filter 320 and polar modulator 310 to the summation node 380 being
different to the delay introduced by the first filter 370 to the
summation node 380.

[0078]Ideally α=1 and β=d=0; in order to allow a conventional
error expression of the amplitude error, A, to be used;

=10(-A/20) (4)

[0079]In this exemplary embodiment, α and β are adjustable by
the polar modulator 310, and δ is fixed as a result of the circuit
design. If β is adjusted through 360 degrees with reasonable
resolution it is always possible to produce a cancellation null at a
frequency ωo=β/δ. The depth of the null is
determined by magnitude α, and the "sharpness" of the null is
determined by the delay error d. If the delay error is 0 then α and
β are adjustable to a pair of values that provides cancellation at
all frequencies. The cancellation, Ψ, in dB is then expressed as:

=10*log(|ξ(t)| 2) (5)

such that

=10*log(1+α2-2*α*cos (β-χδ)) (6)

where (χ=ω-ωo) is the frequency offset from the null
frequency ωo.

[0080]Suppose, within the exemplary embodiment of the active cancellation
device 300 of FIG. 3 that 20 dB of cancellation is specified across the
WiFi band. If the null is placed in the center of the band, maximum
frequency offset χ is (2485-2400)/2=42.5 MHz. With a perfect polar
modulator, the resulting delay mismatch is about 350 ps. With perfectly
matched delays, the resulting polar modulator errors are 0.5 dB and 5
degrees, respectively, for amplitude and phase. These are modest values
for monolithically integrated polar modulators compatible with WiMAX
integrated circuit technologies.

[0081]As discussed in respect of FIG. 3 above the second portion of the
received signal is continuously applied at the summation node 380. In
some circumstances, such as no active WiFi transmitter, the applied
signal from the polar modulator 310 can provide additional noise into the
WiMAX channel. Optionally the circuit path provided by the second filter
320, delay circuit 355 and polar modulator 310 may be configured to
minimize this noise contribution. Approaches to such minimization
including, but not limited to, electrically isolating the second portion
from the summation node 380, and establishing the delay circuit 355 and
polar modulator 310 at an alternate configuration. The decision for
establishing the operational mode for the delay circuit 355 and polar
modulator 310 may provided from one of several sources, including but not
limited to, a measurement of the received power after the second filter
320, a transmitter enable signal from the interfering transmitter, and
network level control protocol signaling.

[0082]FIG. 4A illustrates an exemplary spectrum 400 of a WiFi transmission
signal 440 from a first system operating simultaneously with a WiMAX
transmission signal 430 from a second system. As shown, the first
transmission signal 440 lies within WiFi window 420 of 2400-2485 MHz and
is centered at a frequency 445 that is offset from the WiMAX centre
frequency 435 of the transmitter providing the receive signal 430 in the
collocated WiMAX second system which is operating within the WiMAX window
410 of 2300-2670 MHz.

[0083]FIG. 4B illustrates an exemplary spectrum 4000 of a cancellation
null according to an exemplary embodiment of the invention positioned to
align with the WiFi transmission signal 4400 from a first system
operating simultaneously with a WiMAX transmission signal 4300. As shown,
the first transmission signal 4400 lies within WiFi window 4200 of 2400
MHz-2485 MHz and is centered at a frequency 4450 that is offset from the
WiMAX centre frequency 4350 of the transmitter providing the receive
signal 4300 in the collocated WiMAX second system which is operating
within the WiMAX window 4100 of 2300 MHz-2670 MHz. As shown, the
cancellation null of the cancellation signal 4600 is centered at the same
center frequency 4450 as the WiFi system. Thus the total interferer
signal input power is approximately minimized within this exemplary
embodiment.

[0084]FIG. 5 illustrates an exemplary signal spectrum 5600 fed to a
receiver amplifier, such as amplifier 390 of FIG. 3 after corresponding
cancellation nulling according to an exemplary embodiment of the
invention positioned to align with the WiFi transmission signal 540 from
a first system operating simultaneously with a WiMAX transmission signal
530. As shown, the first transmission signal 540 lies within WiFi window
520 of 2400-2485 MHz and is centered at a frequency 545 that is offset
from the WiMAX centre frequency 535 of the transmitter providing the
receive signal 530 in the collocated WiMAX second system which is
operating within the WiMAX window 510 of 2300-2670 MHz. The first
transmission signal 540 has now been reduced in magnitude from the
received signal, represented by first transmission signal 440 of FIG. 4.

[0085]The coordinate generator 345 provides control signals to the polar
modulator 310 and delay circuit 355, establishing these settings using a
predetermined search algorithm. Considering an exemplary embodiment
wherein there the delay circuit 355 has been set to a constant delay, the
coordinate generator 345 executes a search algorithm. In the exemplary
embodiment of FIG. 6 the coordinate generator 345 executes a
two-dimensional search, one of many potential classic algorithms. Shown
in FIG. 6 is a first stage search 600A displayed as a two dimensional
surface with abscissa Ai 620 representing the amplitude of the in-phase
component of the transmitter signal conversion to form the cancellation
signal, and ordinate Aq 610 representing the quadrature component. As
shown the coordinate generator 345 initially establishes four initial
states 630 for the polar modulator 310. From these the preferred initial
state 640 provides the lowest Rx detected power as determined from the
signal received at the coordinate generator 345 from the Rx power
detector 463. As such the preferred initial state 640 is represented by
states wherein Ai=1xxx and Aq=0xxx.

[0086]The coordinate generator 345 then moves onto second stage 600B,
establishing a restricted search space 652 within a quadrant of the two
dimensional coordinate space. The four second stage states 655 are
established sequentially from which the coordinate generator 345 selects
a second preferred state 650 represented by Ai=11xx; Aq=01xx.

[0087]Now the coordinate generator 345 then moves onto third stage 600C,
establishing a restricted search space 662. Now four third stage states
665 are established sequentially from which the coordinate generator 345
selects a second preferred state 660 represented by Ai=111x; Aq=010x.
Finally, in this exemplary embodiment the coordinate engine performs a
fourth stage 600D of coordinate refinement. In the further restricted
final search space 675 the coordinate generator 345 again establishes
four final states 672 and selects the final preferred state 670
representing coordinates Ai=1110 and Aq=0100.

[0088]It would be apparent to one skilled in the art that whilst WiFi
transceivers, such as WiFi transceiver 130, according to IEEE 802.11b/g,
have essentially been commoditized in the past few years, the
interference problem with WiMAX transceivers, such as WiMAX transceiver
150, is mutual. Although front-end filters are typically used for the
WiFi receiver, the WiMAX out-of-band leakage remains unfilterable and can
present a problem. Consider, an example wherein the WiMAX transceiver,
such as WiMAX transceiver 150, has an output power of +24 dBm,
out-of-band leakage is at -35 dBc and antenna isolation is 20 dB. In this
scenario the WiFi transceiver receives WiMAX leakage at -31 dBm. As such,
it is evident that cancellation is applicable to each transceiver within
a multi-standard device.

[0089]FIG. 7 illustrates an exemplary flow diagram for calibrating an
active cancellation circuit according to an embodiment of the invention
for transmission frequencies of the WiFi standard. The physical delay and
delay mismatch are typically very short in integrated circuit designs,
such that cancellation would be over the breadth of the WiFi channel
spectrum. However, in certain circumstances such as hybrid designs, or
upgrade modules for existing WiMAX transceivers the physical delay and
delay mismatch may be significant such that the cancellation null is
narrow. In these environments, or in applications where WiMAX signals are
being cancelled within a WiFi receiver some calibration of the WiMAX
transceiver may be beneficial. In such scenarios a static delay is
provided and a calibration process obtains the polar modulator settings,
for example. Such a calibration process is shown in FIG. 7.

[0090]As shown, upon starting the calibration process at step 701 the
WiMAX transceiver is enabled and the WiMAX transmitter disabled. At step
702 a counter value N is set to 1, and a test WiFi transmitter is set to
the first channel (N=1) at step 703. With the WiMAX disabled establishing
a near optimum polar modulator setting is achieved by determining when
minimum RF power is received and detected, through steps 705 and 706, at
which point the polar modulator settings are stored in step 707. If the
counter N is equal to the highest channel number, step 709, then the
calibration is stopped at step 708. If not, the counter N is incremented
at step 710, and the calibration cycle repeated for the next channel N+1.
In this manner the settings can be stored for each of the WiFi channels
allowing the null to be placed on either the sole channel present, or the
most significant WiFi transmitter being used, thereby supporting higher
values of cancellation. Such an approach optionally including a WiFi
channel determination circuit within the transceiver, after the WiFi
filter such as first filter 320 of FIG. 3. Optionally, the calibration is
updated for a channel, or established initially using a "trickle"
calibration. Such a "trickle" calibration is optionally performed during
idle times, when the WiMAX transmitter is not actively transmitting
signal data for example. Such a "trickle" calibration allows the polar
modulator settings to mitigate effects of physical changes in the nearby
environment.

[0092]The received wireless signals generated within the antenna 820 by
the wireless signals 825 are first electrically coupled to splitter 830
that provides two splitter output signals. A first output of the splitter
830 is electrically coupled to the WiMAX bandpass filter 840, and
therefrom electrically coupled to the receive amplifier 880 via the
sequence of summation node circuits 862, 864 and 866. The second output
of the splitter 830 is electrically coupled to the WiFi bandpass filter
845. The WiFi filtered portion of the received wireless signals is then
electrically coupled to a second splitter 850, which provides three equal
outputs. A first output of the second splitter 850 is electrically
coupled to a first cancellation circuit 872, which in this exemplary
embodiment comprises a polar modulator, the output of which is coupled to
the first summation node circuit 862.

[0093]The second output of the second splitter 850 is electrically coupled
to a second cancellation circuit 874, similarly comprising a polar
modulator, such that the adjusted signal is then coupled to the second
summation node circuit 864. The third output of the second splitter 850
is electrically coupled to a third cancellation circuit 876, similarly
comprising a polar modulator, such that the adjusted signal is then
coupled to the third summation node circuit 866.

[0094]The output of the receive amplifier 880 is electrically coupled to a
passband limiting filter 815, the output of which is coupled to a second
splitter 825. The primary output of the second splitter 825 is then
electrically coupled to the receiver output port 800A of the multiple
cancellation transceiver 800. The secondary output of second splitter 825
is electrically coupled to a power detector 835, the output of which is
coupled to the measurement port 845D of the coordinate generator 845. The
coordinate generator 845 provides control of the three cancellation
circuits 872, 874 and 876. A first control port 845A of the coordinate
generator 845 being coupled to the coordinate port 872A of the first
cancellation circuit 872. The second and third control ports 845B and
845C of the coordinate generate 845 being coupled to the second and third
cancellation circuits 874 and 876 respectively.

[0095]In this embodiment, each of the cancellation circuits 872, 874, and
876 are set to slightly different settings allowing nulling of the
transmit signal contained within the detected signal with both wider and
deeper nulls in the effective filter profile of the cancellation circuit.
Alternatively where multiple strong interference signals are received the
multiple cancellation circuits 8772, 874, and 876 are optionally
individually tuned for each of the multiple interference signals.
Optionally the second splitter 850 may be replaced with a dynamic
splitter such that the portion of filter WiFi signal provided to each
cancellation circuit 872, 874 and 876 may be adjusted, allowing
management fo the circuit for overall power consumption. Optionally, the
multiple summation node circuits 862, 864 and 866 may be replaced with a
single combiner or summing circuit.

[0096]It is apparent to one skilled in the art that the invention provides
an alternative approach for removing interference within systems where
filtering cannot be provided due to the complexities of implementing the
filter. It would also be apparent that whilst the exemplary embodiments
including filtering elements for separating a WiFi signal from the WiMAX
signals that such filtering may be removed such that a specific WiFi
channel or sub-set of WiFi channels can be cancelled with WiMAX signals
within the WiFi frequency range.

[0097]As is evident many alternative configurations of transmitters,
receivers, transceivers, antenna, multiple standards etc are possible. It
is further apparent that the multiple standards are any of a number of
particular combinations of wireless standards, including but not limited
to GSM/GPRS at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, IEEE 802.11
systems of any variant for WiFi, IEEE 802.16 systems of any variant for
WiMAX, IEEE 802.15 systems or variants for ZigBee, wireless USB,
Bluetooth®, DECT, Wireless Distribution System, and DSRC. Additionally
the wireless systems being cancelled or enhanced by the adoption of
active cancellation are optionally other non-wireless communications
systems such as microwave ovens--emitting typically at 2450 MHz, RFID
tags, global positioning systems (GPS and Galileo), and global navigation
satellite systems (GNSS).

[0098]Though it may seem that the lowest frequency band for WiMAX
according to IEEE 802.16e of 2300-2600 MHz is quite far from the GNSS
bands of 1575±2 MHz (GPS) and 1575±4 MHz (Galileo) the GNSS signals
are extremely low power, in fact the signals are typically within the
noise and GNSS receivers rely on correlation gain to extract the signal
from the noise. As a result a further 25 dB of attenuation in the
splatter from active cancellation is beneficial in minimizing the time
needed to acquire the low level GNSS signal with correlation gain against
the backdrop of noise. Such an exemplary embodiment is described
subsequently in respect of FIGS. 9A and 9B.

[0099]Shown in FIG. 9A is a WiMAX transmitter 920 and a co-located GPS
receiver 910 within a device 900. As shown the WiMAX transmitter
comprises an RF input port 920A for receiving a WiMAX transmit signal
according to IEEE 802.16e having a centre frequency at the 2400 MHz. The
RF input port 920A is electrically coupled to the power amplifier 924
which amplifies the WiMAX transmit signal ready for broadcasting from the
antenna 922, in this exemplary embodiment with a transmit power of +24
dBm.

[0100]The GPS receiver 910 comprises a receiving antenna 912, which being
a broadband antenna receives the intended GPS signal and leakage from the
WiMAX transmitter 920 as represented by the crosstalk path 930. The
electrical signal from the GPS receiver 910 is coupled to a narrow
passband filter 914, which for the GPS standard would have a passband
from 1574-1576 MHz. The filtered signal from the narrow passband filter
914 is then coupled to the GPS low noise amplifier 916 and provided to
the RF output port 910A of the GPS receiver.

[0101]FIG. 9B illustrates an exemplary power spectrum seen at measurement
node 910B of the GPS receiver 910 for the embodiment of actively
cancelling the leakage between the WiMAX transmitter 920 and GPS receiver
910 wherein the crosstalk path 930 attenuates the transmitted signal by
20 dB. Shown within FIG. 9B is first marker 940 representing the centre
frequency 1575 MHz of the GPS receiver 910 and second marker 950
representing the centre frequency 2400 MHz of the WiMAX transmitter 920.
The figure plots power spectral density (PSD) as a function of frequency,
wherein power spectral density is defined as in equation 8 below.

Power Spectral Density=Power in dBm-10*log(Bandwidth) (8)

[0102]Shown in FIG. 9B is the GPS received power spectral density (PSD)
curve 980 representing the GPS received signal, and the WiMAX crosstalk
PSD curve comprising the WiMAX PSD 960 and regrowth PSD 965. Also shown
is the cancelled PSD 970 provided by an active cancellation according to
an exemplary embodiment of the invention such as FIG. 8A.

[0103]Consider, as an example, that the WiMAX transmitter 920 radiates a
transmitted power of +24 dBm within a 10 MHz bandwidth resulting in the
WiMAX PSD 960, using Eq. 8 below of -46 dBm/Hz {-46=+24-10log(10e6)}. The
20 dB attenuation of the transmitted signal by way of the crosstalk path
930 results in the GPS receiver receiving a WiMAX PSD 960 at measurement
node 910B of -66 dBm/Hz at the second marker 950. The narrow passband
filter 914 will filter this signal out, but the WiMAX transmitter
regrowth 965 as shown is only 60 dB down from the WiMAX transmit level.
As such the regrowth PSD 965 is -126 dBm/Hz, and since it is in-band with
the desired GPS signal, represented by GPS receive PSD 980, the narrow
passband filter 914 cannot filter it out.

[0104]If we consider that the upper in-band signal level for the GPS
receiver 910 might be in the range of -80 dBm (corresponding to a GPS
receive PSD 980 of -143 dBm/Hz), then the WiMAX regrowth PSD 965 will
clearly wipe-out the GPS receiver at it's upper limit!

[0105]Now consider that active cancellation is applied between the WiMAX
transmitter 920 and GPS receiver 910, and that the cancellation null is
placed at the first marker 940 of 1575 MHz with a cancellation depth of
25 dB. Now the cancellation null with transmitter regrowth provides the
cancelled PSD 970 of -151 dB/Hz, being -126 dBm/Hz -25 dB, such that the
cancelled PSD 970 is now 8 dB below the GPS receive PSD 980 allowing
recovery of the GPS signal. Further, as the physical thermal noise floor
990 is -174 dBm/Hz such a system does not place significant restrictions
on the noise figure of the GPS low noise amplifier 916, and provides room
for improvements in the cancellation null to still manifest themselves
within the cancelled PSD 970 and increase operating margin for the GPS
receiver 910.

[0106]Numerous other embodiments may be envisaged without departing from
the spirit or scope of the invention.